1. Field of the Invention
The present invention relates to a master guide table for a digital broadcast protocol and a method of broadcasting using the table.
2. Discussion of the Related Art
The Advanced Telephone System Committee (ATSC) has defined a program and system information protocol (PSIP) as a standard for digital television broadcast. In the program and system information protocol (PSIP), the Electronic Program Guide (EPG) and System Information (SI) are defined as one. Namely, the program and system information protocol (PSIP) is the ATSC standard for terrestrial and cable digital broadcast and is defined to provide various information about programs by parsing encoded messages using Moving Picture Experts Group standard ISO/IEC 13818-1 System (MPEG-2) (ATSC Document A/65, 23 Dec. 1997). “Program and System Information Protocol For Terrestrial Broadcast and Cable,” ATSC Document A/65, 23 Dec. 1997 is hereby incorporated by reference for all purposes as if fully set forth herein.
That is, the program and system information protocol is used to transmit or receive audio/video data according to the MPEG-2 video format and AC-3 audio format. Also, the program and system information protocol includes a plurality of tables for transmitting channel information corresponding to each broadcast station, and program information for each channel.
The program and system information protocol can support a main function of selecting a desired channel and for providing audio/video data of the selected channel, and a supplementary function of performing a broadcast guidance service such as an Electronic Program Guide (EPG) for the broadcast programs.
The channel information for selecting the desired channel and packet identification number (PID) for receiving the audio/video data is transmitted to the receiving party through a virtual channel table (VCT), while the information for the Electronic Program Guide (EPG) for the broadcast programs of each channel is transmitted to the receiving party through one or more event information tables (EIT). Further, the program and system information protocol (PSIP) includes a System Time Table (STT) for providing time information, a Rating Region Table (RRT) for forwarding information of geographical region and a corresponding organization and the like to provide a program rating level, an Extended Text Table (ETT) providing an additional description for the channel and broadcast program, and a Master Guide Table (MGT) for managing a version and program identifier for the tables mentioned above.
The tables are transmitted by a data structure called a “section.” That is to say, each table has a section as a basic unit, and a table may be constructed by combining one or more sections.
Each event information table (EIT) has event information for one virtual channel i.e., title, starting time, ending time, caption, and the like. Here, one event generally means a typical television program. Each event information table can be expressed in a general format as EIT-k (k: 0, 1, . . . , 127), and a maximum number if 128 event information tables can be created and transmitted. Each event information table EIT-k may have multiple instances, each of which contains information for one virtual channel. Specifically, the program and system information protocol PSIP may have at least 4 and a maximum of 128 event information tables EITs, and each event information table EIT provides event information for a specific time zone.
FIG. 1 is a diagram illustrating a bit stream syntax of a general master guide table (MGT). The master guide table (MGT) is transmitted in a single section format as a table, listing version number, length, and program identifier (PID) for all of the tables of the program and system information protocol (PSIP), except the System Time Table (STT).
With reference to FIG. 1, the master guide table (MGT) has a table identifier field “table_id” of “0xC7,” and a section length field “section length” which represents the section length. A version number field “version_number” represents a version value of the master guide table (MGT), the version value is increased by 1 module 32 when the contents of the master guide table (MGT) are changed.
Meanwhile, a section number field “section-number” represents a corresponding section number, a last section number field “last_section_number” represents a last section number of the master guide table (MGT), and the two fields each have a fixed value of “0x00”, since the MGT is always one section long. A table definition field “tables_defined” defines a number of tables (0-65535) which will appear in a “for_loop” statement afterward.
A table type field “table_type” in the “for_loop” statement represents the type of table. For example, a value of each table information type field “table_type” for the event information tables EIT0-EIT127 is 0x0100-0x017F. A table type program identifier field “table_type_PID” defines the program identifier (PID) for the table type field “table_type”, and a table type version number field “table_type_version_number” designates the version number defined in each table type field “table_type.” For instance, a next event information table (EIT) has a value increased by 1 with respect to the value of the present event information table (EIT).
A descriptors length field “descriptors_length” represents the whole length in bytes for representing a descriptor of the master guide table (MGT). An error correction field, CRC—32, represents a 32 bit cyclical redundancy check (CRC) value for error correction.
Here, the program identifier (PID) of the general format EIT-k event information table must have an equivalent value as specified as the master guide table (MGT), and has to define a unique value in the table type program identifier field “table_type PID” contained in the master guide table (MGT).
For instance, a broadcast station can transmit broadcast information from the present time through the next 16 days to the digital television receiver by means of the event information tables EIT-0, EIT-1, EIT-2, . . . , EIT-127. That is, an event information table (EIT) has contents for events corresponding to a period of 3 hours, and a total of 128 event information tables (EITs) can be transmitted in the field. Here, the event information table EIT-0 means a table for an event of the present time, and is shifted every 3 hours (i.e., 0:00, 03:00, 06:00, etc.).
At this time, if an electronic program guide EPG service is to be performed, the digital television receiver has to store the contents of the event information tables by parsing the event information tables. To achieve this, the digital television receiver constructs a database for performing the electronic program guide (EPG) service by gathering the event information tables (EITs) received from the broadcast station.
FIG. 2 is a diagram illustrating a schedule information table for programs broadcasting over four virtual channels of one physical channel.
In FIG. 2, 1-A, 1-B . . . , 1-E designate program titles which will be broadcast in a channel 51-1, and 2-A, . . . , 4-F designate other program titles for the virtual channels.
In the figure, the lines with the dot at the end designate the current time zone, while the lines with the arrows designate the absolute time at which the general format EIT-k (k=0-127) event information table is shifted in FIG. 2, respectively.
According to the ATSC standard within a 24-hour day, there are 8 absolute times for shifting the contents of the event information table, i.e., 0:00, 3:00, 6:00, 9:00, 12:00, 15:00, 18:00, 21:00.
Meanwhile, the present time zones in FIG. 2 are divided into 5 zones based on the absolute time for shifting the general format EIT-k of the event information table. At this stage, the contents of the general format EIT-k event information table are shifted to the other general format EIT-(k−1) event information table according to each time zone. Here, k is a positive integer of between 0 and 127.
For instance, if the data in the event information table EIT-0 based on the absolute time for shifting the contents of the event information table EIT is expired because the data belongs to a past program, the contents of the event information table EIT-1 are shifted to the event information table EIT-0.
As described, when the present time zone is the absolute time for shifting event information table EIT-k, the digital television receiver has to receive the entire event information tables (EITs) all over again, in order to perform the service of the Electronic Program Guide EPG.
That is, the version number of the master guide table MGT is changed whenever the contents of the tables defined in the table type of the “for_loop” statement are changed. For example, if the contents of the event information table EIT-k are changed, the version number of the master guide table MGT is changed. Also, if the contents of the event information tables EIT, i.e. the program contents, are shifted without change, the version number of the master guide table MGT is also changed.
The television receiver performs an update operation with the contents of the event information table EIT-k by receiving the event information table EIT-k again and receiving the contents of the database again when the version number of the master guide table MGT is changed, while the table type program identifier field “table_type_PID” defines the event information table EIT-k.
This description clearly means that the database should be updated perfunctorily at every absolute time shifting of the event information table.
Accordingly, there is a drawback in the related art in that unnecessary time for updating the database is consumed, even if the contents of the database for the program constructed in a previous time zone are not changed. This time consumption places a heavier burden on the digital television receiver or the cable broadcast receiver, which operates as the receiving party.
Further, viewers have to wait for a long time with patience to receive the service of the Electronic Program Guide (EPG).